The invention relates to a process and an apparatus for producing sponge iron from iron-oxide-containing material in lump form by direct reduction in a reduction shaft using a reducing gas.
When producing sponge iron, also referred to as direct reduction iron, by direct reduction, the reduction shaft is charged from above with iron oxides in lump form, such as pellets and/or lump ores, through which a rising reducing gas is made to flow on the basis of the counterflow principle. The reducing gas that is introduced into the reduction shaft, preferably being at a temperature of 750 to 900° C., containing dust and rich in carbon monoxide and hydrogen, in particular containing 70 to 90% CO and H2, is preferably produced in a fusion gasifier or in some other gas generator. In this way, the iron oxide in lump form is reduced completely or partially to sponge iron and a degree of metallization of from 80% to over 95% of the sponge iron can be achieved.
In the apparatuses and processes that are known from the prior art, the reducing gas is introduced at the circumference of the reduction shaft, for example by means of an annular duct that is formed by refractory bricks, known as a bustle duct. When the reducing gas is introduced by means of such a bustle duct, however, less reducing gas reaches the middle of the reduction shaft, and so the degree of metallization in the outer region is higher than it is toward the middle of the reduction shaft. Since a poured fill with a lower degree of metallization has a greater bulk weight than such a fill with a higher degree of metallization, and also breaks down to a greater extent, the motion of the filling process is concentrated toward the middle of the reduction shaft. This centrally concentrated motion has the effect that the uneven distribution of the specific amount of reducing gas is further exacerbated. The uneven distribution of the reducing gas is all the greater the larger the diameter of the reduction shaft and the greater the amount of dust contained in the reducing gas. Furthermore, the bustle duct formed by refractory bricks requires a lining, which is costly, susceptible to wear and therefore keeps having to be renewed.
In DE2628447A1, in addition to the bustle duct, a central feeding device below the level of the bustle duct is described. According to EP0904415A1, additional reducing gas inlets in the form of downwardly open ducts or obliquely downwardly directed lines with an open inner end are likewise located below the level of a bustle duct.
Although these apparatuses provide a better supply of reducing gas toward the middle, the reduction shaft with the bustle duct and gas distribution ducts in the middle is costly and still has the disadvantage that the reducing gas is introduced at the same pressure at two different levels, as a specific result of which more reducing gas per m2 is introduced through the higher inlet, since the upward path of the gas is shorter there. Less reducing gas specifically means, however, a lower degree of metallization of the fill in the middle of the reduction shaft.
DE 28 10 657 discloses a reduction shaft which has in addition to a bustle pipe devices for the introduction of process gases, such as for example natural gas. Disadvantages in this case are the uneven introduction of the reducing gas via the bustle pipe and the high cost of the apparatus.
WO 00/36159 describes a reduction shaft in which reducing gas is introduced at two levels or in two zones. Disadvantages are, in particular, the great technical cost of the plant and the high requirements for controlling the introduction of the reducing gas.